This is a dumb question, but do epa stoves actually burn creosote before it becomes solid? Is that one of the gasses that light off the secondaries? My curiosity is because a more efficient stove is going to send less heat up the chimney right? Does that put you in danger of building creosote at a low burn rate (with cat/ secondaries lit)? Thanks for any thoughts.
actually its not a dumb question at all. to be simplistic about it , "smoke" is simply wood that aint burnt yet. stack gasses for the most part are also unburned fuel
the thing about creosote is that its not just the amount of smoke being exhausted by the stove, creosote is formed when the products of incomplete combustion are not completely evacuated by the chimney then allowed to mix with moisture at a temperature below 211F.
one of the things to remember when it comes to the issues with creosote in "smoke dragons" is that the methods people used to try to get longer burn times out of them ended up being the biggest cause for excessive creosote buildup. with an old pre-epa unit the only thing one could do to slow the burn time down to achieve an overnight burn was to deny air to the primary fire. this does a couple things in an old unit which you do not typically get with a modern stove.
1. lower stack temps, since there is no secondary burn in an old tech stove the incomplete burn created by denial of primary air results in a cooler fire and lower stack temps.
2. the amount of smoke created by this type of fire results in an exteremely incomplete level of combustion.
so you are putting a lot of fuel in the stack and also running a lower stack temp allowing moisture which IS a byproduct of woodburning even with seasoned wood (though much worse with wet wood) the rapid building of creosote will happen. this starts to reduce the diameter of the flue as this stuff layers up, now the dangerous part of this is that when you reduce diameter you increase temperature in the exhaust stream. so once enough concentration is present add a hot fire and boom, there you go to a chimney fire.
the real advantages of a modern unit stem from not only the ability to burn a much higher percentage of the stuff which usually creates creosote but in doing so burn in such a way as to create higher exhaust temps with lower volume of flow. this is the big difference. a modern stove is designed in such a way as to deny a larger portion of primary air (as with the old tech) while at the same time , introducing secondary air downstream if you will from the primary fire. this allows a slow burn which would normally plug up a chimney with the reburn after the fire which not only burns away the largest portion of unspent fuel, but also BOOSTS exhaust temperature to maintain stack temps above the creosote zone. so, you get the "long burn times" without plugging up your chimney and polluting the air.
the added bonus (and really where the boosted efficiency comes into play is this) you are producing a "hot fire" output, with a "slow burn" fire. simply releasing more energy from the fuel at a slower pace.
hope this helps ya!
